Number of Subarrays With LCM Equal to K
A medium-tier problem at 40% community acceptance, tagged with Array, Math, Number Theory. Reported in interviews at Unity and 0 others.
You get an array and a target integer K. Count how many contiguous subarrays have an LCM (least common multiple) equal to K. This problem looks like a straightforward enumeration until you realize naive LCM computation across every subarray will timeout. Unity has asked it. With a 40% acceptance rate, most candidates either nail the optimization or walk away. The trick isn't hard once you see it, but if you blank during the live assessment, StealthCoder surfaces a working solution in seconds while the proctor sees nothing.
Companies that ask "Number of Subarrays With LCM Equal to K"
Number of Subarrays With LCM Equal to K is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe brute force approach checks all O(n²) subarrays and computes LCM for each, but LCM calculations compound and you'll TLE. The real insight: LCM of a subarray can only decrease or stay the same as you shrink the subarray. So for each starting position, iterate only while the LCM is still a valid divisor of K. Once LCM exceeds K, stop. This cuts the inner loop dramatically in practice. You'll compute LCM efficiently using GCD (gcd(a, b) = a * b / lcm(a, b)). The problem mixes Array, Math, and Number Theory because you need to understand LCM properties and divisibility, not just loop counting. If this hits your live OA and you stall on the divisor pruning idea, StealthCoder runs invisibly and hands you a working solution so you move on.
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Number of Subarrays With LCM Equal to K recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Number of Subarrays With LCM Equal to K interview FAQ
Why does brute force fail on this problem?+
Every subarray needs an LCM calculation, and computing LCM for every pair takes time. With n up to 50,000, O(n²) subarrays times log operations per LCM exceeds time limits. You need a smarter iteration that prunes impossible subarrays early using divisibility.
Is this problem still asked at top companies?+
Yes. Unity is confirmed in recent reports. The 40% acceptance rate suggests it's a medium-to-hard screen question, not a warm-up. If you see it on your OA, you're hitting the serious part of the assessment.
What's the key optimization trick?+
LCM of a subarray is monotonic: it never decreases as you add elements. So if LCM exceeds K, you can skip that subarray and all longer extensions. This pruning cuts the inner loop from O(n) to roughly O(log n) in practice, making the solution feasible.
Do I need advanced number theory for this?+
No. You need to know GCD and how to compute LCM via GCD (lcm(a, b) = a * b / gcd(a, b)). Most languages have built-in GCD. The hard part is the subarray pruning strategy, not the math itself.
How does this connect to the Array and Math topics?+
Array covers the iteration and subarray enumeration. Math covers LCM, GCD, and divisibility logic. You're not doing heavy number theory proofs; you're using number properties to optimize array iteration, which is why both topics appear together here.
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